The present invention relates to a semiconductor laser device, more specifically a semiconductor laser device capable of realizing high power and high reliability, and to an optical disk recording and reproducing apparatus using the same.
In recent years, with demands for faster and larger-capacity semiconductor laser devices applied to optical communications devices and optical recording apparatuses, research and development have been promoted for improving various properties of the semiconductor laser devices.
Among the semiconductor laser devices, those having an oscillation wavelength of 780 nm band for use in optical disk reproducing apparatuses and optical disk recording and reproducing apparatuses such as CD and CD-R/RW are conventionally made of AlGaAs based materials and typically have ridge stripe shape.
Generally in such semiconductor laser device, in superimposing a current constriction layer, a portion in the vicinity of a lateral face of a ridge stripe is positioned below an overhang of a contact layer, which prevents material gas from sufficiently reaching the vicinity of the lateral face of the ridge stripe. Further, due to plane orientation of the lateral face of the ridge stripe, there is an area whose crystal growth rate is slow. As a result, the portion in the vicinity of the lateral face of the ridge stripe is not fully filled up and a hollow portion is generated therein.
The above has been disclosed in Japanese Patent Laid-Open Publication HEI No. 3-64980, in which a means for eliminating the hollow portion has been proposed to solve a problem that the hollow portion has a low refractive index and therefore a single transverse mode oscillation is difficult to produce, and the like. A schematic view thereof is shown in FIG. 8, with reference to which outlined description will be made hereinbelow.
The semiconductor laser device is so structured that on top of a GaAs substrate 501, there are laminated in sequence an AlGaAs first cladding layer 502, an AlGaAs active layer 503, an AlGaAs second cladding layer 504, and a GaAs contact layer 505. Further, there is spattered an SiO2 film (unshown), which is formed into a stripe shape by a usual photo step. Then, with the SiO2 film as a mask, the contact layer 505 and the second cladding layer 504 are etched by chemical etching to make the second cladding layer 504 into ridge stripe shape.
With the SiO2 film as a mask for selective growth, there is formed a GaAs current constriction layer 506 on the both sides of the ridge stripe-shaped second cladding layer 504. After that, the SiO2 film is removed and the other contact layer 505 is laminated on the entire surface of the already formed contact layer 505 and the GaAs current constriction layer 506 so that the laminated contact layer 505 is integrated with them.
In the above conventional example, the hollow portion is eliminated to stabilize transverse mode oscillation. However, an inventor of the present invention actually manufactured as an experiment an AlGaAs based high-output semiconductor laser device based on the conventional technique, as a result of which it was confirmed that a maximum optical output thereof is approx. 180 mW, and end face destruction occurs at this optical output level. This is because the presence of active Al tends to generate Al oxide on a laser end face, which prevents implementation of higher output, higher reliability and longer life.
Also in the above conventional example, the contact layer 505 and the second cladding layer 504 are etched into ridge stripe shape with an etchant modified to prevent the stripe-shaped contact layer 505 from protruding from the ridge-strip-shaped second cladding layer 504 in lateral direction like an overhang. This method, however, suffers difficulty in management of etchant and etching time.